There was no evidence of criminal involvement in their deaths and tests on air and water at the hotel found nothing unusual, Mr Sadek said.

Travel company Thomas Cook commissioned specialists to examine the hotel after the deaths, with tests showing normal carbon monoxide levels near the couple's room and normal levels of chlorine in the swimming pool.

However, tests on the food and hygiene standards "identified a high level of E.coli and staphylococcus bacteria", the firm said.

Thomas Cook said in a statement that it noted the chief prosecutor's announcement following post-mortems.

"We have not yet seen the full report and we will need time for our own experts to review it," the travel firm said.

"We are deeply saddened by the tragic deaths of John and Susan Cooper. "We will continue to offer every support to their daughter Kelly and the rest of their family."

Thomas Cook evacuated 300 guests from the hotel as a precaution after the deaths. Mrs Ormerod has previously said she found her parents seriously ill in their room.